Plastic shell for protecting electric appliance and manufacturing method thereof

Abstract

The invention relates to the technical field of plastic shells, and discloses a plastic shell for protecting an electric appliance and a manufacturing method thereof, the plastic shell comprises the following raw materials: polypropylene, a compound flame retardant, a reinforcing additive, sodium dodecyl benzene sulfonate, an antioxidant 1076 and oxidized polyethlene wax; wherein the compound flame retardant is a three-source-in-one intumescent flame retardant synthesized by taking a polylactic acid-glycolic acid copolymer as a carbon source, 2-amino-4, 6-dihydroxypyrimidine as a gas source and ethyl dichlorophosphate as an acid source, so that the flame retardant property of the plastic shell is remarkably improved; the reinforcing additive is prepared by grafting 7-hydroxycoumarin to the surface of the sisal fiber, so that the mechanical strength of the plastic shell is effectively improved, the use field of the plastic shell is greatly widened through the comprehensive exertion of the properties, and the overall service life of an electric appliance is prolonged.

Description

Technical Field

[0001] The invention relates to the technical field of plastic shells, and in particular to a plastic shell for protecting electrical appliances and a manufacturing method thereof. Background Art

[0002] With the advancement of science and technology and the improvement of people's living standards, electrical appliances have gradually become a part of people's lives. Plastics are widely used in electrical equipment due to their unique performance advantages and processing convenience. The casing is an important part of electrical appliances, and its main function is to provide physical protection for electrical appliances. At present, most electrical appliance casings are plastic casings. By wrapping the internal components and circuit boards of the appliances, the plastic casing can prevent external impacts, dust, moisture and other environmental factors from damaging the appliances, thereby extending the service life and stability of the appliances.

[0003] Polypropylene has become the preferred material for preparing electrical appliance casings due to its advantages such as light weight, non-toxicity, odorlessness, good insulation, low price and easy processing. With the development of science and technology, people have increasingly stringent requirements on the performance of electrical appliance casings. During use, electrical appliances may generate open flames or high temperatures due to electric arcs, sparks or short circuits. Polypropylene is a flammable material and will produce molten droplets during the combustion process, releasing a large amount of heat and toxic gases, thereby causing fire accidents and limiting its application in a wider range of fields. Therefore, plastic casings need to have excellent flame retardant properties. In addition, existing electrical appliance plastic casings need to have excellent mechanical strength to resist external impact and extrusion, prevent damage to electrical appliances due to collision or extrusion during transportation, installation and use, and better isolate and protect the circuits and components inside the electrical appliances, thereby extending the overall service life of the electrical appliances.

[0004] In the prior art, optimizing the basic material is one of the main ways to improve the performance of plastic shells. For example, the invention patent with the publication number CN113444317B discloses a method for preparing a high-gloss flame-retardant polypropylene material. The invention uses the prepared 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide grafted glycidol as a flame retardant component and participates in the preparation process of the polypropylene material, so that the prepared polypropylene material has excellent flame retardancy and can be widely used in the manufacture of electrical housings such as household appliances, outdoor appliances, and industrial and mining appliances, with high economic value and social benefits. Therefore, the plastic shell can be modified by preparing a filling component with excellent flame retardancy and mechanical strength to obtain a high-performance plastic shell. Summary of the invention

[0005] In order to solve the problems mentioned in the background technology, the object of the present invention is to provide a plastic shell for protecting electrical appliances and a manufacturing method thereof.

[0006] The purpose of the present invention can be achieved by the following technical solutions:

[0007] A plastic shell for protecting electrical appliances comprises the following raw materials in parts by weight: 60-70 parts of polypropylene, 4-6 parts of compound flame retardant, 5-9 parts of reinforcing additive, 1-3 parts of sodium dodecylbenzene sulfonate, 1-2 parts of antioxidant 1076, and 2-3 parts of oxidized polyethylene wax.

[0008] Furthermore, the preparation method of the composite flame retardant comprises the following steps:

[0009] A1: Under nitrogen protection, polylactic acid-glycolic acid copolymer, 2-amino-4,6-dihydroxypyrimidine and dimethyl sulfoxide solution are mixed and stirred evenly, and then an activator and a condensing agent are added. After the addition is completed, the temperature is raised to 65-75°C, and the mixture is stirred for 4-7 hours at the same temperature. The heating is stopped and the nitrogen is removed. The mixture is cooled to room temperature and then discharged to obtain an intermediate material.

[0010] A2: The intermediate material and ethyl acetate are added to a reactor filled with nitrogen in sequence. After stirring evenly, ethyl dichlorophosphate and an accelerator are added. Under stirring conditions, the system temperature is raised to 60-70°C and kept warm for 3-6 hours. After the material is cooled naturally, the material is discharged to obtain a compound flame retardant.

[0011] Furthermore, in step A1, the activator is any one of 1-hydroxybenzotriazole, 4-dimethylaminopyridine or N-hydroxysuccinimide.

[0012] Furthermore, in step A1, the condensing agent is any one of N,N'-dicyclohexylcarbodiimide, 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide or N,N'-diisopropylcarbodiimide.

[0013] Furthermore, in step A2, the promoter is any one of pyridine or triethylamine.

[0014] Furthermore, the preparation method of the reinforcing additive comprises the following steps:

[0015] AA1: ultrasonically dispersing sisal fiber in a toluene solution to form a dispersion, adding halogenated isocyanate and dibutyltin dilaurate to the dispersion under continuous nitrogen conditions, stirring evenly, reacting at 50-70° C. for 2-4 hours, and after the reaction is completed, centrifuging to separate solid materials, washing the solid materials, and vacuum drying to obtain modified sisal fiber;

[0016] AA2: Add modified sisal fiber to N,N-dimethylformamide, ultrasonically treat for 20 to 40 minutes, introduce nitrogen, and then add 7-hydroxycoumarin and triethylamine. After the addition is completed, turn on the heating. After the system temperature reaches 70 to 80°C, stir at a constant temperature for 5 to 7 hours, filter, collect the product, wash, and dry to obtain a reinforcing additive.

[0017] Furthermore, in step AA1, the halogenated isocyanate is any one of 2-chloroethyl isocyanate or 3-chloropropyl isocyanate.

[0018] Furthermore, in step AA2, the mass ratio of the modified sisal fiber to 7-hydroxycoumarin is 1:0.1-0.3.

[0019] A method for manufacturing a plastic shell for protecting an electrical appliance comprises the following steps:

[0020] Step 1: Add polypropylene, compound flame retardant, reinforcing additive, sodium dodecylbenzene sulfonate, antioxidant 1076, and oxidized polyethylene wax into a high-speed kneader, knead at 110-120° C. for 30-50 minutes, and then place in a cooling mixer and cool to 30-40° C. to obtain a mixed material;

[0021] Step 2: Add the obtained mixture into a granulator for extrusion granulation, set the temperature of the first zone of the granulator barrel to 80-90°C, the temperature of the second zone to 130-160°C, the temperature of the third zone to 170-180°C, the temperature of the fourth zone to 120-140°C, and the head temperature to 170-180°C to obtain masterbatch;

[0022] Step 3: The masterbatch obtained above is injection molded by an injection molding machine to obtain a plastic shell.

[0023] Furthermore, in step three, the process conditions of the injection molding are: controlling the injection material temperature to be 180-220° C., the injection pressure to be 40-60 MPa, and the injection speed to be 20-40 mm / s.

[0024] Beneficial effects of the present invention:

[0025] (1) The present invention adds a compound flame retardant and a reinforcing additive during the preparation of the plastic shell, so that the limiting oxygen index of the prepared plastic shell can reach up to 32.6%, the tensile strength can reach up to 53.4MPa, and the impact strength can reach up to 32.6KJ / m 2 , has good flame retardant properties and mechanical strength, which greatly broadens the application field of plastic casings and extends the overall service life of electrical appliances.

[0026] (2) The present invention adds a compound flame retardant during the preparation process of the plastic shell, which can significantly improve the flame retardant properties of the plastic shell. The polylactic acid-hydroxyacetic acid copolymer in the compound flame retardant can be used as a carbon source, 2-amino-4,6-dihydroxypyrimidine can be used as a gas source, and ethyl dichlorophosphate can be used as an acid source to synthesize a "three-source-in-one" intumescent flame retardant. When a fire occurs, a dense foam carbon layer can be formed to generate a large amount of non-toxic and non-flammable gas, which is added into the foam carbon layer through adsorption, thereby making the layer non-flammable, heat-insulating, and oxygen-isolating, thereby ultimately preventing the spread and propagation of the flame, and avoiding fire accidents caused by the burning of the plastic shell due to electric arcs, sparks or short circuits during the use of electrical appliances, thereby broadening its application in a wider range of fields.

[0027] (3) The present invention prepares a reinforcing additive as a reinforcing agent for a plastic shell. After being organically modified, the sisal fiber has good interface properties with the polypropylene matrix and can be relatively evenly dispersed in the polypropylene matrix to form a good filling effect. On the one hand, the advantages of the sisal fiber can be used to effectively improve the mechanical strength of the plastic shell, avoid damage to the electrical appliance due to collision or extrusion during transportation, installation and use, and better isolate and protect the circuits and components inside the electrical appliance. On the other hand, the rigid ring grafted on the surface of the sisal fiber can further play a reinforcing role, so that the prepared plastic shell has excellent mechanical strength, thereby extending the overall service life of the electrical appliance.

[0028] Of course, any product implementing the present invention does not necessarily need to achieve all of the advantages described above at the same time. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings required for describing the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other accompanying drawings can be obtained based on these accompanying drawings without paying creative work.

[0030] Figure 1 This is an infrared spectrum test chart of the intermediate material and the compound flame retardant prepared in Example 1 of the present invention.

[0031] Figure 2 This is an infrared spectrum test chart of the reinforcing additive prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0032] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0033] Example 1

[0034] 1. Preparation of compound flame retardant

[0035] A1: Under nitrogen protection, 5 g of polylactic acid-glycolic acid copolymer, 1.2 g of 2-amino-4,6-dihydroxypyrimidine and dimethyl sulfoxide solution were mixed and stirred evenly, and then 0.08 g of 4-dimethylaminopyridine and 0.05 g of N,N'-diisopropylcarbodiimide were added. After the addition was completed, the temperature was raised to 70°C, and the mixture was stirred for 6 hours. The heating was stopped and the nitrogen was removed. After cooling to room temperature, the mixture was discharged to obtain an intermediate material.

[0036] A2: 5 g of the intermediate material and ethyl acetate were added to a reactor filled with nitrogen in sequence. After stirring evenly, 1.4 g of ethyl dichlorophosphate and 0.1 g of triethylamine were added. The system temperature was raised to 65°C under stirring conditions and kept warm for 4 hours. After the material was naturally cooled, it was discharged to obtain a composite flame retardant.

[0037] The intermediate materials and compound flame retardants were analyzed by infrared spectroscopy using the WQF-200 Fourier transform infrared spectrometer from Beijing Rayleigh Analytical Instruments Co., Ltd. Figure 1 As shown by Figure 1 It can be seen that in the infrared spectrum of the intermediate material, 3280cm -1 The absorption peak of hydroxyl group OH appears at 3324 cm -1 The absorption peak of NH in the amide bond appears at 1655 cm -1 The absorption peak of C=O in the amide bond appears at 1760 cm -1 The absorption peak of the ester group C=O appears at 1409 cm -1 The absorption peak of CN appears at 1605cm -1 The absorption peak of C=N appears at 3310cm -1 The absorption peak of NH in the amide bond appears at 1650cm -1 The absorption peak of C=O in the amide bond appears at 1765cm -1 The absorption peak of the ester group C=O appears at 1415 cm -1 The absorption peak of CN appears at 1610 cm -1 The absorption peak of C=N appears at 1280cm-1 The absorption peak of P=O appeared at 1061cm -1 The characteristic absorption peak of POC appears at

[0038] Technical principle: In the compound flame retardant, firstly, since 2-amino-4,6-dihydroxypyrimidine contains active amino substituents in its structure, under the action of 4-dimethylaminopyridine and N,N'-diisopropylcarbodiimide, it can undergo amidation reaction with the carboxyl active functional groups in the structure of polylactic acid-glycolic acid copolymer, thereby introducing 2-amino-4,6-dihydroxypyrimidine into the structure of polylactic acid-glycolic acid copolymer to obtain an intermediate material; secondly, under the action of triethylamine, the hydroxyl groups in the structure of the intermediate material can further react with the phosphorus oxychloride groups in the structure of ethyl dichlorophosphate to obtain a compound flame retardant.

[0039] 2. Preparation of reinforcing additives

[0040] AA1: 3 g of sisal fiber was ultrasonically dispersed in a toluene solution to form a dispersion. Under continuous nitrogen conditions, 0.8 g of 2-chloroethyl isocyanate and 0.03 g of dibutyltin dilaurate were added to the dispersion, stirred evenly, and reacted at 60° C. for 3 h. After the reaction was completed, solid materials were separated by centrifugation, washed, and vacuum dried to obtain modified sisal fiber.

[0041] AA2: Add 3 g of modified sisal fiber to N,N-dimethylformamide, ultrasonically treat for 30 min, introduce nitrogen, and then add 1 g of 7-hydroxycoumarin and 0.05 g of triethylamine. After the addition is completed, turn on the heating. After the system temperature reaches 75°C, stir at a constant temperature for 6 h, filter, collect the product, wash, and dry to obtain a reinforcing additive.

[0042] The WQF-200 Fourier transform infrared spectrometer from Beijing Rayleigh Analytical Instruments Co., Ltd. was used to analyze the reinforcing additives by infrared spectroscopy. Figure 2 As shown by Figure 2 It can be seen that in the infrared spectrum of the reinforcing additive, 3330cm -1 The absorption peak of -NH in the carbamate group appears at 1691 cm -1 The absorption peak of C=O in the carbamate group appears at 3050cm -1 The absorption peak of CH on the benzene ring appears at 1040cm -1 The absorption peak of ether bond COC appears at

[0043] Technical principle: In the reinforcing additive, first, under the catalytic action of dibutyltin dilaurate, the hydroxyl groups on the surface of the sisal fiber react with the isocyanate groups in the structure of 2-chloroethyl isocyanate, thereby modifying the surface of the sisal fiber with halogen functional groups to obtain modified sisal fiber; secondly, under the action of triethylamine, the halogen functional groups on the surface of the sisal fiber are used as active sites, and the mechanism that the halogen functional groups can undergo substitution reactions with the hydroxyl groups in the structure of 7-hydroxycoumarin is utilized to graft 7-hydroxycoumarin onto the surface of the sisal fiber to obtain the reinforcing additive.

[0044] 3. Preparation of plastic shell

[0045] Step 1: Add 60g polypropylene, 4g compound flame retardant, 5g reinforcing additive, 1g sodium dodecylbenzene sulfonate, 1g antioxidant 1076, and 2g oxidized polyethylene wax into a high-speed kneader, knead for 30min at 110°C, and then place in a cooling mixer and cool to 30°C to obtain a mixed material;

[0046] Step 2: Add the obtained mixture into a granulator for extrusion granulation, set the temperature of the first zone of the granulator barrel to 80°C, the temperature of the second zone to 130°C, the temperature of the third zone to 170°C, the temperature of the fourth zone to 120°C, and the head temperature to 170°C to obtain masterbatch;

[0047] Step 3: The masterbatch obtained above is injection molded by an injection molding machine, and the material temperature of the injection molding is controlled to be 180° C., the injection pressure is 40 MPa, and the injection speed is 40 mm / s to obtain a plastic shell.

[0048] Example 2

[0049] Preparation of plastic shell

[0050] Step 1: Add 65g of polypropylene, 5g of compound flame retardant, 7g of reinforcing additive, 2g of sodium dodecylbenzene sulfonate, 1.5g of antioxidant 1076, and 2.5g of oxidized polyethylene wax into a high-speed kneader, knead for 40min at 115°C, and then place in a cooling mixer and cool to 35°C to obtain a mixed material;

[0051] Step 2: Add the mixture obtained above into a granulator for extrusion granulation, set the temperature of the first zone of the granulator barrel to 85°C, the temperature of the second zone to 145°C, the temperature of the third zone to 175°C, the temperature of the fourth zone to 130°C, and the head temperature to 175°C to obtain a masterbatch;

[0052] Step 3: The masterbatch obtained above is injection molded by an injection molding machine, and the material temperature of the injection molding is controlled to be 200° C., the injection pressure is 50 MPa, and the injection speed is 50 mm / s to obtain a plastic shell.

[0053] The preparation method of the compound flame retardant and the reinforcing additive is the same as that in Example 1.

[0054] Example 3

[0055] Preparation of plastic shell

[0056] Step 1: Add 70g of polypropylene, 6g of compound flame retardant, 9g of reinforcing additive, 3g of sodium dodecylbenzene sulfonate, 2g of antioxidant 1076, and 3g of oxidized polyethylene wax into a high-speed kneader, knead for 50min at 120°C, and then place in a cooling mixer and cool to 40°C to obtain a mixed material;

[0057] Step 2: Add the mixture obtained above into a granulator for extrusion granulation, set the temperature of the first zone of the granulator barrel to 90°C, the temperature of the second zone to 160°C, the temperature of the third zone to 180°C, the temperature of the fourth zone to 140°C, and the head temperature to 180°C to obtain masterbatch;

[0058] Step 3: The masterbatch obtained above is injection molded by an injection molding machine, and the material temperature of the injection molding is controlled to be 220° C., the injection pressure is 60 MPa, and the injection speed is 60 mm / s to obtain a plastic shell.

[0059] The preparation method of the compound flame retardant and the reinforcing additive is the same as that in Example 1.

[0060] Comparative Example 1

[0061] Preparation of plastic shell

[0062] Step 1: Add 65g of polypropylene, 5g of compound flame retardant, 2g of sodium dodecylbenzene sulfonate, 1.5g of antioxidant 1076, and 2.5g of oxidized polyethylene wax into a high-speed kneader, knead for 40min at 115°C, and then place in a cooling mixer and cool to 35°C to obtain a mixed material;

[0063] Step 2: Add the mixture obtained above into a granulator for extrusion granulation, set the temperature of the first zone of the granulator barrel to 85°C, the temperature of the second zone to 145°C, the temperature of the third zone to 175°C, the temperature of the fourth zone to 130°C, and the head temperature to 175°C to obtain a masterbatch;

[0064] Step 3: The masterbatch obtained above is injection molded by an injection molding machine, and the material temperature of the injection molding is controlled to be 200° C., the injection pressure is 50 MPa, and the injection speed is 50 mm / s to obtain a plastic shell.

[0065] The preparation method of the composite flame retardant is the same as that in Example 1.

[0066] Comparative Example 2

[0067] Preparation of plastic shell

[0068] Step 1: Add 65g of polypropylene, 7g of reinforcing additive, 2g of sodium dodecylbenzene sulfonate, 1.5g of antioxidant 1076, and 2.5g of oxidized polyethylene wax into a high-speed kneader, knead for 40min at 115°C, and then place in a cooling mixer and cool to 35°C to obtain a mixed material;

[0069] Step 2: Add the mixture obtained above into a granulator for extrusion granulation, set the temperature of the first zone of the granulator barrel to 85°C, the temperature of the second zone to 145°C, the temperature of the third zone to 175°C, the temperature of the fourth zone to 130°C, and the head temperature to 175°C to obtain a masterbatch;

[0070] Step 3: The masterbatch obtained above is injection molded by an injection molding machine, and the material temperature of the injection molding is controlled to be 200° C., the injection pressure is 50 MPa, and the injection speed is 50 mm / s to obtain a plastic shell.

[0071] The preparation method of the reinforcing additive is the same as that in Example 1.

[0072] Comparative Example 3

[0073] Preparation of plastic shell

[0074] Step 1: Add 65g of polypropylene, 5g of compound flame retardant, 5g of sisal fiber, 2g of 7-hydroxycoumarin, 2g of sodium dodecylbenzene sulfonate, 1.5g of antioxidant 1076, and 2.5g of oxidized polyethylene wax into a high-speed kneader, knead for 40min at 115°C, and then place in a cooling mixer and cool to 35°C to obtain a mixed material;

[0075] Step 2: Add the mixture obtained above into a granulator for extrusion granulation, set the temperature of the first zone of the granulator barrel to 85°C, the temperature of the second zone to 145°C, the temperature of the third zone to 175°C, the temperature of the fourth zone to 130°C, and the head temperature to 175°C to obtain a masterbatch;

[0076] Step 3: The masterbatch obtained above is injection molded by an injection molding machine, and the material temperature of the injection molding is controlled to be 200° C., the injection pressure is 50 MPa, and the injection speed is 50 mm / s to obtain a plastic shell.

[0077] The preparation method of the composite flame retardant is the same as that in Example 1.

[0078] Comparative Example 4

[0079] Preparation of plastic shell

[0080] Step 1: Add 65 g of polypropylene, 2 g of sodium dodecylbenzene sulfonate, 1.5 g of antioxidant 1076, and 2.5 g of oxidized polyethylene wax into a high-speed kneader, knead at 115° C. for 40 min, and then place in a cooling mixer and cool to 35° C. to obtain a mixed material;

[0081] Step 2: Add the mixture obtained above into a granulator for extrusion granulation, set the temperature of the first zone of the granulator barrel to 85°C, the temperature of the second zone to 145°C, the temperature of the third zone to 175°C, the temperature of the fourth zone to 130°C, and the head temperature to 175°C to obtain a masterbatch;

[0082] Step 3: The masterbatch obtained above is injection molded by an injection molding machine, and the material temperature of the injection molding is controlled to be 200° C., the injection pressure is 50 MPa, and the injection speed is 50 mm / s to obtain a plastic shell.

[0083] Performance testing:

[0084] The plastic shells prepared in Examples 1 to 3 of the present invention and Comparative Examples 1 to 4 were made into samples that met the specifications. The samples were subjected to a combustion performance test according to GB / T 2406.2-2009 "Determination of Combustion Behavior of Plastics by Oxygen Index Method Part 2: Room Temperature Test" to evaluate the flame retardant properties of the plastic shell; the samples were subjected to a tensile strength test according to GB / T 1040.1-2018 "Determination of Tensile Properties of Plastics Part 1: General Principles"; the samples were subjected to an impact strength test according to GB / T1843-2008 "Determination of Izod Impact Strength of Plastics". The specific test results are shown in Table 1:

[0085] Table 1 - Performance Test

[0086] Limiting oxygen index (%) Tensile strength(MPa) <![CDATA[Impact strength (KJ / m 2 )]]> Example 1 32.3 52.6 32.1 Example 2 32.6 53.4 32.6 Example 3 31.9 52.1 31.8 Comparative Example 1 29.4 41.8 22.9 Comparative Example 2 22.5 49.5 29.7 Comparative Example 3 30.2 44.3 25.3 Comparative Example 4 19.7 39.7 20.2

[0087] From the test results in Table 1, it can be seen that the plastic shells prepared in Examples 1 to 3 are added with compound flame retardants and reinforcing additives, and the limiting oxygen index of the plastic shell is higher than 30%, the tensile strength is higher than 50MPa, and the impact strength is higher than 30KJ / m 2, all of which have excellent flame retardant properties and mechanical strength; no reinforcing additives are added to the plastic shell prepared in Comparative Example 1, and the mechanical strength of the plastic shell is poor compared with that in the embodiment; no compound flame retardant is added to the plastic shell prepared in Comparative Example 2, the limiting oxygen index decreases significantly, and the flame retardant performance of the plastic shell is not as good as that in the embodiment; compound flame retardant, sisal fiber and 7-hydroxycoumarin are added to the plastic shell prepared in Comparative Example 3, and compared with the embodiment, the flame retardant performance of the plastic shell is better, but the mechanical strength performance is average. It is speculated that this may be because the surface of the sisal fiber is not modified, and its compatibility with the matrix is ​​poor, resulting in a decrease in the mechanical strength of the plastic shell; no compound flame retardant and reinforcing additives are added to the plastic shell prepared in Comparative Example 4, so the flame retardant performance and mechanical strength performance of the plastic shell are the worst.

[0088] The above contents are merely examples and explanations of the concept of the present invention. The technicians in this technical field may make various modifications or additions to the specific embodiments described or replace them in a similar manner. As long as they do not deviate from the concept of the invention or exceed the scope defined by the claims, they should all fall within the protection scope of the present invention.

Claims

1. A plastic casing for protecting an electrical appliance, characterized in that: The invention comprises the following raw materials in parts by weight: 60-70 parts of polypropylene, 4-6 parts of compound flame retardant, 5-9 parts of reinforcing additive, 1-3 parts of sodium dodecylbenzene sulfonate, 1-2 parts of antioxidant 1076 and 2-3 parts of oxidized polyethylene wax.

2. A plastic casing for protecting an electrical appliance according to claim 1, characterized in that: The preparation method of the composite flame retardant comprises the following steps: A1: Under nitrogen protection, polylactic acid-glycolic acid copolymer, 2-amino-4,6-dihydroxypyrimidine and dimethyl sulfoxide solution are mixed and stirred evenly, and then an activator and a condensing agent are added. After the addition is completed, the temperature is raised to 65-75°C, and the mixture is stirred for 4-7 hours at the same temperature. The heating is stopped and the nitrogen is removed. The mixture is cooled to room temperature and then discharged to obtain an intermediate material. A2: The intermediate material and ethyl acetate are added to a reactor filled with nitrogen in sequence. After stirring evenly, ethyl dichlorophosphate and an accelerator are added. Under stirring conditions, the system temperature is raised to 60-70°C and kept warm for 3-6 hours. After the material is cooled naturally, the material is discharged to obtain a compound flame retardant.

3. A plastic casing for protecting an electrical appliance according to claim 2, characterized in that: In step A1, the activator is any one of 1-hydroxybenzotriazole, 4-dimethylaminopyridine or N-hydroxysuccinimide.

4. A plastic casing for protecting an electrical appliance according to claim 2, characterized in that: In step A1, the condensing agent is any one of N,N'-dicyclohexylcarbodiimide, 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide or N,N'-diisopropylcarbodiimide.

5. A plastic casing for protecting an electrical appliance according to claim 2, characterized in that: In step A2, the promoter is any one of pyridine or triethylamine.

6. A plastic casing for protecting an electrical appliance according to claim 1, characterized in that: The preparation method of the reinforcing additive comprises the following steps: AA1: ultrasonically dispersing sisal fiber in a toluene solution to form a dispersion, adding halogenated isocyanate and dibutyltin dilaurate to the dispersion under continuous nitrogen conditions, stirring evenly, reacting at 50-70° C. for 2-4 hours, and after the reaction is completed, centrifuging to separate solid materials, washing the solid materials, and vacuum drying to obtain modified sisal fiber; AA2: Add modified sisal fiber to N,N-dimethylformamide, ultrasonically treat for 20 to 40 minutes, introduce nitrogen, and then add 7-hydroxycoumarin and triethylamine. After the addition is completed, turn on the heating. After the system temperature reaches 70 to 80°C, stir at a constant temperature for 5 to 7 hours, filter, collect the product, wash, and dry to obtain a reinforcing additive.

7. A plastic casing for protecting an electrical appliance according to claim 6, characterized in that: In step AA1, the halogenated isocyanate is any one of 2-chloroethyl isocyanate or 3-chloropropyl isocyanate.

8. A plastic casing for protecting an electrical appliance according to claim 6, characterized in that: In step AA2, the mass ratio of the modified sisal fiber to 7-hydroxycoumarin is 1:0.1-0.

3.

9. A method for manufacturing a plastic casing for protecting an electrical appliance as claimed in claim 1, characterized in that: The following steps are involved: Step 1: Add polypropylene, compound flame retardant, reinforcing additive, sodium dodecylbenzene sulfonate, antioxidant 1076, and oxidized polyethylene wax into a high-speed kneader, knead at 110-120° C. for 30-50 minutes, and then place in a cooling mixer and cool to 30-40° C. to obtain a mixed material; Step 2: Add the obtained mixture into a granulator for extrusion granulation, set the temperature of the first zone of the granulator barrel to 80-90°C, the temperature of the second zone to 130-160°C, the temperature of the third zone to 170-180°C, the temperature of the fourth zone to 120-140°C, and the head temperature to 170-180°C to obtain masterbatch; Step 3: The masterbatch obtained above is injection molded by an injection molding machine to obtain a plastic shell.

10. A method for manufacturing a plastic casing for protecting an electrical appliance according to claim 9, characterized in that: In step three, the process conditions of the injection molding are: controlling the injection material temperature to be 180-220° C., the injection pressure to be 40-60 MPa, and the injection speed to be 20-40 mm / s.

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